WASHINGTON (WUSA9) -- Prosecutors' long-running investigation of political corruption at D.C. City Hall is showing signs of heating up.

The US Attorney has just filed new charges against finance consultant Stanley Straughter. Earlier in the day, accountant Lee Calhounpleaded guilty Thursday to campaign law violations.

Both men are cooperating as the probe continues.

Powerhouse defense attorney Ed MacMahonsays there'splenty more to come. His client, Lee Calhoun, pleaded guilty to making bogus straw campaign contributions, morethan $120,000 in contributions, made in Calhoun's name, but with money that belonged to his boss.

"What you are going to see now for awhile this summer is people that trusted Jeffrey Thompson and did things, made campaign contributions on his behalf, all being brought through the system and many of them dealt with the same way Mr Calhoun was today," says MacMahon.

Jeffrey Thompson is allegedly the man behind Mayor Vince Gray's $650,000 unreported shadow campaign... the man whose home and offices were raided last year by FBI and the IRS.

US Attorney Ron Machen says this kind of political corruption can threaten the integrity of the Democratic process. The big question now, whether he will file charges against Jeffrey Thompson, and whether those charges might then lead to Mayor Vince Gray.

The Mayor has studiously avoided answering questions about his involvement in his own shadow campaign. And he was out talking education, even as he was heckled by a handful of parents.

Calhoun's lawyer says it's pretty clear how this political corruption cases usually go. "From general experience, they build these cases going up. And you guys know that as well."

Prosecutors are lining up the little guys. Could the big guys be far behind?